## 5 Steps to a 5: AP Physics C (2016)

### STEP __2__

### Determine Your Test Readiness

__CHAPTER__ **4 Fundamentals Quizzes**

__CHAPTER__ **5 Take a Diagnostic Test**

### CHAPTER 4

### Fundamentals Quizzes

**IN THIS CHAPTER**

**Summary:** To test your readiness for the exam, take these short quizzes on these two fundamental topics of AP Physics.

**Key Ideas**

Find out what you know—and what you don”t know—about mechanics.

Find out what you know—and what you don”t know—about electricity and magnetism.

Focus your exam preparation time *only* on the areas you don”t already know well.

These short quizzes may be helpful if you”re looking for some additional review of the most fundamental topics in AP Physics. If you can get all these right, you are READY for the exam!

The answers are printed at the end of this chapter.

**Mechanics Quiz**

** 1 .** What is the mass of a block with weight 100 N?

** 2 .** Give the equations for two types of potential energy, identifying each.

** 3 .** When an object of mass

*m*is on an incline of angle

*θ*, one must break the weight of an object into components parallel and perpendicular to the incline.

- What is the component of the weight parallel to the incline?_________
- What is the component of the weight perpendicular to the incline?_________

** 4 .** Write two expressions for work, including the definition of work and the work-energy principle.

** 5 .** Quickly identify as a vector or a scalar:

** 6 .** Name at least four things that can NEVER go on a free-body diagram.

** 7 .** Write two expressions for impulse. What are the units of impulse?

** 8 .** In what kind of collision is momentum conserved? In what kind of collision is kinetic energy conserved?

** 9 .** What is the mass of a block with weight

*W*?

** 10 .** A ball is thrown straight up. At the peak of its flight, what is the ball”s acceleration? Be sure to give both magnitude and direction.

** 11 .** A mass experiences a force vector with components 30 N to the right, 40 N down. Explain how to determine the magnitude and direction (angle) of the force vector.

** 12 .** Write the definition of the coefficient of friction,

*μ*. What are the units of

*m*?

** 13 .** How do you find acceleration from a velocity-time graph?

** 14 .** How do you find displacement from a velocity-time graph?

** 15 .** How do you find velocity from a position-time graph?

** 16 .** An object has a positive acceleration. Explain

*briefly*how to determine whether the object is speeding up, slowing down, or moving with constant speed.

** 17 .** Given the velocity of an object, how do you tell which direction that object is moving?

** 18 .** When is the gravitational force on an object

*mg*? When is the gravitational force

*Gm*

_{1}m

_{2}/

*r*

^{2}?

** 19 .** What is the direction of the net force on an object that moves in a circle at constant speed?

** 20 .** Under what conditions is the equation at

^{2}valid? Give a specific situation in which this equation might seem to be valid, but is NOT.

**Electricity and Magnetism Quiz**

** 1 .** Given the charge of a particle and the electric field experienced by that particle, give the equation to determine the electric force acting on the particle.

** 2 .** Given the charge of a particle and the magnetic field experienced by that particle, give the equation to determine the magnetic force acting on the particle.

** 3 .** What are the units of magnetic flux? What are the units of EMF?

** 4 .** A wire carries a current to the left, as shown below. What is the direction and magnitude of the magnetic field produced by the wire at point

*P*?

** 5 .** When is the equation

*kQ/r*

^{2}valid? What is this an equation for?

** 6 .** The electric field at point

*P*is 100 N/C; the field at point

*Q*, 1 meter away from point

*P*, is 200 N/C. A point charge of +1 C is placed at point

*P*. What is the magnitude of the electric force experienced by this charge?

** 7 .** Can a current be induced in a wire if the flux through the wire is zero? Explain.

** 8 .** True or false: In a uniform electric field pointing to the right, a negatively charged particle will move to the left. If true, justify with an equation; if false, explain the flaw in reasoning.

** 9 .** Which is a vector and which is a scalar: electric field and electric potential?

** 10 .** Fill in the blank with either “parallel” or “series”:

- Voltage across resistors in ______ must be the same for each.
- Current through resistors in ______ must be the same for each.
- Voltage across capacitors in ______ must be the same for each.
- Charge stored on capacitors in ______ must be the same for each.

** 11 .** A uniform electric field acts to the right. In which direction will each of these particles accelerate?

- proton
- positron (same mass as electron, but opposite charge)
- neutron
- anti-proton (same mass as proton, but opposite charge)

** 12 .** A uniform magnetic field acts to the right. In which direction will each of these particles accelerate, assuming they enter the field moving toward the top of the page?

- proton
- positron (same mass as electron, but opposite charge)
- neutron
- anti-proton (same mass as proton, but opposite charge)

** 13 .** How do you find the potential energy of an electric charge?

**Answers to Mechanics Quiz**

** 1 .** Weight is

*mg*. So, mass is weight divided by

*g*, which would be 100 N/(10 N/kg) = 10 kg.

** 2 .** PE =

*mgh*, gravitational potential energy;

PE = ½*kx* ^{2} , potential energy of a spring.

** 3 .** i.

*mg*sin

*θ*is parallel to the incline.

*mg*cos*θ*is perpendicular to the incline.

** 4 .** The definition of work is work = force times parallel displacement. The work-energy principle states that net work = change in kinetic energy.

** 5 .** vectors: acceleration, force, momentum, velocity, displacement

scalars: speed, work, mass, kinetic energy

** 6 .** Only forces acting on an object and that have a single, specific source can go on free-body diagrams. Some of the things that cannot go on a free-body diagram but that students often put there by mistake:

** 7 .** Impulse is force times time interval, and also change in momentum. Impulse has units either of newton·seconds or kilogram·meters/second.

** 8 .** Momentum is conserved in

*all*collisions. Kinetic energy is conserved only in elastic collisions.

** 9 .** Using the reasoning from question #1, if weight is

*mg*, then

*m*=

*W*/

*g*.

** 10 .** The acceleration of a projectile is

*always g*; i.e., 10 m/s

^{2}, downward. Even though the velocity is instantaneously zero, the velocity is still changing, so the acceleration is

*not*zero. (By the way, the answer “−10 m/s

^{2}” is wrong unless you have clearly and specifically defined the down direction as negative for this problem.)

** 11 .** The magnitude of the resultant force is found by placing the component vectors tip-to-tail. This gives a right triangle, so the magnitude is given by the Pythagorean theorem, 50 N. The angle of the resultant force is found by taking the inverse tangent of the vertical component over the horizontal component, tan

^{−1}(40/30). This gives the angle measured from the horizontal.

__12__ .

friction force divided by normal force. *μ* has no units.

** 13 .** Acceleration is the slope of a velocity-time graph.

** 14 .** Displacement is the area under a velocity-time graph (i.e., the area between the graph and the horizontal axis).

** 15 .** Velocity is the slope of a position-time graph. If the position-time graph is curved, then instantaneous velocity is the slope of the tangent line to the graph.

** 16 .** Because acceleration is not zero, the object

*cannot*be moving with constant speed. If the signs of acceleration and velocity are the same (here, if velocity is positive), the object is speeding up. If the signs of acceleration and velocity are different (here, if velocity is negative), the object is slowing down.

** 17 .** An object

*always*moves in the direction indicated by the velocity.

** 18 .** Near the surface of a planet,

*mg*gives the gravitational force. Newton”s law of gravitation,

*Gm*

_{1}

*m*

_{2}/

*r*

^{2}, is valid everywhere in the universe. (It turns out that

*g*can be found by calculating

*GM*

_{planet}

*/R*

_{planet}

^{2}, where

*R*

_{planet}is the planet”s radius.)

** 19 .** An object in uniform circular motion experiences a

*centripetal*, meaning “center seeking,” force. This force must be directed to the center of the circle.

** 20 .** This and all three kinematics equations are valid only when acceleration is constant. So, for example, this equation can NOT be used to find the distance travelled by a mass attached to a spring. The spring force changes as the mass moves; thus, the acceleration of the mass is changing, and kinematics equations are not valid. (On a problem where kinematics equations aren”t valid, conservation of energy usually is what you need.)

**Answers to Electricity and Magnetism Quiz**

__1__ .*F* = *qE* .

__2__ .*F* = *qvB* sin *θ* .

** 3 .** Magnetic flux is

*BA*, so the units are tesla·meters

^{2}(or, alternatively, webers). EMF is a voltage, so the units are volts.

** 4 .** Point your right thumb in the direction of the current, i.e., to the left. Your fingers point in the direction of the magnetic field. This field wraps around the wire, pointing into the page above the wire and out of the page below the wire. Since point

*P*is below the wire, the field points out of the page.

** 5 .** This equation is only valid when a point charge produces an electric field. (Careful—if you just said “point charge,” you”re not entirely correct. If a point charge experiences an electric field produced by something else, this equation is irrelevant.) It is an equation for the electric field produced by the point charge.

** 6 .** Do

*not*use

*E*=

*kQ*/

*r*

^{2}here because the electric field is known. So, the source of the electric field is irrelevant—just use

*F*=

*qE*to find that the force on the charge is (1 C)(100 N/C) = 100 N. (The charge is placed at point

*P*, so anything happening at point

*Q*is irrelevant.)

** 7 .** Yes! Induced EMF depends on the

*change*in flux. So, imagine that the flux is changing rapidly from one direction to the other. For a brief moment, flux will be zero; but flux is still changing at that moment. (And, of course, the induced current will be the EMF divided by the resistance of the wire.)

** 8 .** False. The negative particle will be

*forced*to the left. But the particle could have entered the field while moving to the right … in that case, the particle would continue moving to the right, but would slow down.

** 9 .** Electric field is a vector, so fields produced in different directions can cancel. Electric potential is a scalar, so direction is irrelevant.

** 10 .** Voltage across resistors in parallel must be the same for each.

Current through resistors in series must be the same for each.

Voltage across capacitors in parallel must be the same for each.

Charge stored on capacitors in series must be the same for each.

** 11 .** The positively charged proton will accelerate with the field, to the right.

The positively charged positron will accelerate with the field, to the right.

The uncharged neutron will not accelerate.

The negatively charged anti-proton will accelerate against the field, to the left.

** 12 .** Use the right-hand rule for each:

The positively charged proton will accelerate into the page.

The positively charged positron will accelerate into the page.

The uncharged neutron will not accelerate.

The negatively charged anti-proton will accelerate out of the page.

** 13 .** If you know the electric potential experienced by the charge, PE =

*qV*.

**What Do I Know, and What Don”t I Know?**

I”ll bet you didn”t get every question on both of these fundamentals quizzes correct. That”s okay. The whole point of these quizzes is for you to determine where to focus your study.

It”s a common mistake to “study” by doing 20 problems on a topic on which you are already comfortable. But that”s not studying … that”s a waste of time. You don”t need to drill yourself on topics you already understand! It”s also probably a mistake to attack what for you is the toughest concept in physics right before the exam. Virtually every student has that one chapter they just don”t get, however hard they try. That”s okay.

The fundamentals quizzes that you just took can tell you exactly what you should and should not study. Did you give correct answers with full confidence in the correctness of your response? In that case, you”re done with that topic. No more work is necessary. The place to focus your efforts is on the topics where either you gave wrong answers that you thought were right, or right answers that you weren”t really sure about.

Now, take the diagnostic test. Once you”ve used the fundamentals quizzes and diagnostic test to identify the specific content areas you want to work on, proceed to the review in __Chapters 9__ –__20__ . Read a chapter, work through the examples in the chapter, and attempt some of the problems at the end of the chapter. Then come back to these fundamentals quizzes. When you respond to every question confidently, you are ready.